I've experienced this periodically since my early 20's - generally in hindsight I realise it was: real life getting in the way, burnout, lack of interest (I was interested in the idea, but on some fundamental level - not the activity) - also occasionally just a feeling of Groundhog Day (ie. Some code tasks can just feel a little too familiar - even if novel, and that saps my joy)

Either way, at the time it was quite worrying - even disturbing - especially when there was work to be done, so think I can relate

Generally I was able to reverse it by working on something which really stimulated me - even hacking away on some goofy personal project after hours - and that kind of bootstrapped me back into a place where I could easily attain flow for "harder" tasks. Can't recommend that highly enough, that and realising that I had different stimulus needs to previously - changing up my coding music, or even foregoing it and switching to mynoise.net yielded some excellent results, or reducing distractions (try periodically disabling system notifications)

That said, if you're really concerned probably see a doc just to rule out any funny business

Ps. Best of luck with it, crossing fingers for you